There seems to be a resurgence in interest in the achromatic scopes. If so what are some of the reasons do you think. I have a Vixen A 105 M. I bought it because I wanted a 4" scope with good optical figure for doubles and planets. The color correction is good and I'm pleased with it. But part of my reason was just the classic appeal of a good 4" inch achro.

"There seems to be a resurgence in interest in the achromatic scopes."

Nah, it's just that the folks who normally haunt the Classics forum have finally discovered that there are other forums on CN.

I "get" achromats when a good one can be had at a given aperture for materially less money than a like-apertured ED doublet or triplet. Indeed when I bought my Antares 105/1500 it was just $650 and the competing 4" ED doublets from Synta were $900. What I don't "get" though is paying more for an achromat of a given aperture than you could pay for a decent quality RD triplet or doublet. Other than indulging one's curiosity, I feel there's little logic in such a move.

Apochromats will be phased out eventually.....like all other types of transitional technology.

Then, Nostalgic Man, suffering from a kind of poverty of the imagination, will seek out achromats above all other telescopic relics from the past. For these were the first kinds of refractors that were corrected well enough to give both an accurate and picturesque simulacrum of the heavenly bodies, as history so nobly attests to.

Achromats have a future (because they are the true gems in the box); apochromats don't.

Enjoy your Vixen achromat; one day it will fetch a whole lot more than a TEC, Tak or AP.

Possibly people are realising that a decent achro is a decent scope. If designed reasonably they can produce some good viewing at a reasonable cost.

Maybe the imaging side carried over too much into the visual side, as in imaging you cannot put up with CA. Whereas in visual some people simply don't worry about CA and on dim objects the CA may well not be noticable. Why pay 3-5x for something that is of no concern or relevance.

You will have to accept a longer scope and I would say there is a practical limit to length, guess about 1.2 metre focal length.

The available glass types are now more varied, perhaps manufacturers do not use an ED glass, but they might use one that is closer to ED then what was around 15-20 years ago. Still achro but better then previously available.

Refractors are illogical any way you slice it. So picking an achromat over an apo for dso observing is no more crazy than picking a refractor over a dob for said purpose. If you want a 6 inch refractor and don't want to sell one of your kids to buy it, the achromat is the only game in town. You use your scopes for their intended purpose. Play to the strengths of the design and you will be happy. I just picked a 6" achromat and I'm having fun exploring many classic dso's that my other scopes just can't show off, like this scope. So yes I think they are, and should make a come back.

Well I like my Vixen achro well enough but fetch a higher price some day than a TAK or TEC??? I really doubt that. Now if you have a TAK or TEC that you want to swap to get my Vixen I'd be glad to help you out.

I don't think so. They do have their niches, which they serve well. One thing they do better than anything else in my experience, is wide-field deep-sky observing. They also cool down quickly and so if you have only a limited amount of time for lunar-planetary observing, a refractor is the way to go. They are also superior for solar observing. Double star observing is also one of their traditional niches.

There are times when I miss my second telescope, a Parks 80mm f/11 achromat/equatorial. I gave it to a relative after acquiring the fluorite, along with a couple of oculars I considered expendable. With it, I once observed Venus from about five in the morning when it was still dark until the sun approached high noon, the planet's surface at that point appearing as sand, just visible, peppered, grainy, the mount motorised only in right ascension and positioned partly on the grass, partly on the walk at our home in midtown Memphis. Earlier, just before dawn, an unsuspecting fellow, known to be challenged, was walking down the sidewalk. As he approached, he suddenly caught sight of me, crouched down, peering through my refractor. He jumped back a bit, veered off the sidewalk, off the curb into the street, then back onto the path and resumed his walk. I'll never forget his startled expression, sustained for several moments as he passed, nor the face of Venus alight that morning in 1992.

That being related, I'm wanting another achromat, with said Antares f/15 appearing more and more desirable, especially with its Japanese doublet, if I'm not mistaken, and costing less than that of the Skylight produced in London.

Technological advancement is absolute and does not grant exceptions. Just as the achromat replaced Galileans and Keplerians, the aprochromat has just as surely and irreversibly replaced the achromat. One day, something else will replace the apochromat, but by then the achromat will be as well represented in use as the Galileans and Keplerians are today. Know where a guy can buy a quality Keplerian these days?

There's nothing wrong with make-believe, of course. It can be fun. Who doesn't like dressing in Elizabethan garb, hefting a tankard in one hand and turkey leg in the other, and talking funny? But that doesn't signal a return to relevance of Elizabethan culture, fashion or speech mannerisms. It's just recreational "pretending".

Just as the achromat rendered the Keplerian and other singlets largely irrelevant, so too the apochromat has rendered the achromat largely irrelevant (in a commercial sense), and indeed something new will eventually relegate the apochromat to oblivion as well. But that's tomorrow. Today, the relevance of refractors is all about apochromats. Far more energy is devoted to making better aporchromats than any other refractor design presently.

In thirty years, the pretentious re-enactors will be using A-Ps, TECs and Taks, and find all kinds of justifications for clinging to those designs, other than technical superiority. Today, though, the refractor anachronists cling to achromats. But don't feel bad. You should hear what those Keplerian fanboys are saying about both achromats and apochromats!

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. . . That being related, I'm wanting another achromat, with said Antares f/15 appearing more and more desirable, especially with its Japanese doublet, if I'm not mistaken, and costing less than that of the Skylight produced in London. Alan

If you can swing it, Alan, go for the Skylight instead. I've had an Antares f/15 (actually f/14.3) and now have the Skylight f/13. The Antares did a pretty good job, but the views through the Skylight are much more crisp, and it will handle a whole lot more magnification than the Antares before the image starts to break down. The construction of the Skylight is much, much better, and the focuser is a huge improvement over the one provided on the Antares scope. I hesitated at the cost, but it was well worth it.

I never would have believed it if I hadn't seen it for myself. A well-figured achromatic lens is really something special. If you've ever looked through a Zeiss Telementor or the 80/1200 Zeiss, you'll understand what I'm referring to.

And you can dispense with the Elizabethan garb -- they only wear that in some strange area of California located north of San Francisco.

The achromat hasn't replaced the galileian and keplerian telescopes, but improved them. The optical layout of the modern apochromatic telescope, with a positive eyepiece, is still, technically, called a keplerian telescope. Likewise, you can buy small achromatic galileian binoculars for use in theaters and operas or even as ultra-specialized 2.8x40 glasses for observing the milky way with 28° TFOV. There's a tremendous difference in their level of sophistication, but all modern telescopes and binoculars are based on the same basic optical principles Galileo and Kepler found.

Know where a guy can buy a quality Keplerian these days?

Almost everywhere. Even shopping malls. OK, you said "quality", so maybe not shopping malls...

the apochromat has rendered the achromat largely irrelevant (in a commercial sense)

No, not yet. Achromats still outnumber apochromats by a huge number. Think binoculars, spottingscopes and rifle scopes. Rarely are these apochromats and they outsell amateur telescopes by huge amounts.

[quote name="jrbarnett"]Technological advancement is absolute and does not grant exceptions. Just as the achromat replaced Galileans and Keplerians, the aprochromat has just as surely and irreversibly replaced the achromat.

Jim,

At a guess ?? more achromats have been produced in the last 20 years, than the preceeding 300 ! So how they have been replaced with apos is an interesting assumption.

I know everyone is looking for the latest big thing !
Just like diffractive optics were going to make all other lens types obsolete 40 years ago , now we have this development.

To me it has to do with the economy. When I bought my AT-102ED it was affordable, the AT-111 was not, nor are the 106's or other triplets. When I bought my C6R OTA it's because I CANNOT afford or even think about a 6" in an ED doublet, let alone triplet. And being a visual observer only, CA isn't that big a deal. Today, if I were looking at a 4", the only choice for me would be an achromat since the ED's have all but disappeared and I can't afford the 4" triplets, especially for visual use grab-and-go.

Well, I'd be very surprised if (e.g.) one could see (meaning "visually") the $1300+ difference between an ES 127 Achro and Apo if you had them side by side looking at (e.g) The Orion Nebula. No doubt the Apo would have drastically reduced CA if viewing the moon. How about the $???? difference between ES's 152 mm Achro and Apo.

There is a resurgence of interest in achromats, thanks in part to Neil and his interesting writings, and companies like Skylight in the UK who are prepared to put them together very nicely, albeit for quite a few £'s.

Over the past 24 months I've been able to directly compare good 4" and 5" achromats with my Vixen 102mm F/6.5 and Skywatcher 120mm F/7.5 ED doublets and I've concluded that I won't be moving back (and that's how I see it) to achromats.

In short my ED's did everything the achromats did a little better and are much easier to mount steadily to boot.

My ED's are both older models so both cost me less than scopes such as the Skylight achromats and Antares 105mm F/15's.

It's good to find these things out for yourself though, if you can, and let the views you get be your guide

I don't think so. They do have their niches, which they serve well. One thing they do better than anything else in my experience, is wide-field deep-sky observing. They also cool down quickly and so if you have only a limited amount of time for lunar-planetary observing, a refractor is the way to go. They are also superior for solar observing. Double star observing is also one of their traditional niches.

Clear skies!
Thomas, Denmark

It's almost like you read my mind.

I use my Sky-Watcher 80mm achro for solar, lunar and planetary viewing. I love the tack-sharp images that it produces and the focuser is butter-smooth.

Back in 2003, fate blessed me, two-folded, with my first apochromat: a Takahashi FS-102 with a superb doublet, the front element being of calcium fluorite, a crystal rather than glass, and a rear element of low-dispersion glass(ED?). One way in which it was fortunate, it was on sale at the time for $1899, down from $2200 or so. Then, later, in 2006 or '07 with the beginning of the rise in cost of calcium fluorite blanks, it was replaced by the current TSA-102, a triplet(crown, ED, flint or crown?). No matter, for the FS-102 is decidedly superior given it's a tad brighter, with better contrast and sharpness, however in exchange it does exhibit slightly more spurious colour on brighter objects, though just slightly. I'll take the before-mentioned advantages instead.

The current four-inch triplet is described within advertisements as a "New Design", perhaps a ploy designed to mask Takahashi's necessary exodus from true fluorite, however Takahashi still produces fluorite elements, but only in 60mm and 90mm sizes, and then skips to this leviathan...THE FET...

Imagine all the used four-inch Takahashi fluorite refractors on sale in this ad or that, right now, with perhaps many of the sellers patently oblivious given the above, unless they're selling to acquire a larger one, whether it be an FS-152 or the astronomically-priced TOA-150, the latter a non-fluorite but optically excellent nonetheless in comparison to the former, though not nearly as aesthetic in that it is an evolution beyond pomp and circumstance.

Get them while they last, before someone else gets a clue...

On the other hand, there's just something about a plain and simple, good, old-fashioned crown and flint achromat that beckons. I can't explain it, as it's ineffable, or perhaps it's the child seemingly lost in all of us, regardless of technological advancements and monetary considerations; Elizabethan ruffs even, which I would sport in a heartbeat, but only on Halloween or in a past life.

My first telescope was a 60mm Sears "Discoverer", when I was 7 or 8, and the first view was of Saturn through the recently-restored 20mm Kellner pictured within my avatar. Saturn appeared very sharp, though in a weird, fluorescent shade of green I'll never forget.

My father bought my mother a brand new Meade Model 285 Refractor for her birthday when I was in my mid-teens, and paid WAY too much money for it. Looking through the 25mm M.A. EP produced decent lunar views, but when I placed the cheap, cheesy 9mm EP into the diagonal, for a high-power view, the moon looked like it had a severe case of the chicken pox. Needless to say, I was hooked, but it would be another decade before I would have the disposable income or time to pursue this hobby.

I am sure the achromats will stay around as cheap alternatives for a long time to come, in my view they never left the amateur scene!They will still be sold as entry level telescopes or for aficionados that are ready to spend more on hand figured achros with long focal lengths.

But let's be honest the market place has changed with the relatively cheap and always improving ED's out of China. Better color correction with shorter easier to mount tubes are hard to pass - especially when available on the used market.

I personally do not plan to go back to my first and second scope which were 70mm and 100mm Achros by now I am spoiled by more capable APO's!